1. Field of the Invention
The invention relates to electronic signal processing of digital video information, particularly to encoding of compressed video signals according to MPEG format.
2. Description of Background Art
MPEG ("Motion Picture Experts Group") refers to standard for encoding and decoding moving pictures and associated audio (MPEG I and II) as adopted by International Standardization Organization (Geneva) and specified in ISO/IEC 13818-2, Recommendation ITU-T. H.262 (1995E) as well as in related ISO/IEC 11172-2 (1993), which is referred to therein such publications being hereby incorporated by reference.
Previous video information was formatted, transmitted and stored largely in analog form. Recent implementation of video equipment, media and signaling, however, have shifted increasingly from analog to more desirable digitized paradigm. Digital video offers, not just improved functionality and quality, but substantially lower cost for program producers and consumers as emerging digital video standards, namely MPEG, facilitate delivery of advanced low-cost video applications to mainstream markets. Additionally, compelling technical and economic benefits arise when digital video systems and components are implemented in integrated circuits using conventional manufacturing processes, such as Complementary Metal Oxide Semiconductor (CMOS).
In context of MPEG (I and II) specification, various complex processing algorithms are defined for digitally encoding and decoding compressed video bitstream, such as motion-compensated predictive coding, discrete cosine transform, and variable length coding. Particularly, with respect to motion compensation during encoding process, wherein, among other things, two-dimensional motion vectors are used for predicting or estimating video picture data, namely frame or field information, by providing offsets into past and/or future reference frames or fields, predictions are formed, as specified, from previously decoded pictures which are combined, for example, with certain coefficient data to recover final decoded samples.
Although MPEG contemplates such motion-compensated coding scheme, the standard does not specify necessarily a particular way in which motion estimation is to be achieved, so long as correct syntax for motion vectors is followed. Hence, various approaches at estimating motion have been set forth. Haskell, et al. describe motion-compensated prediction for MPEG encoding using estimate averaging or weighted choices (U.S. Pat. No. 5,619,256), or using disparity estimates based on forward and backward predictions (U.S. Pat. No. 5,612,735). Iu describes in U.S. Pat. No. 5,293,229 MPEG encoding prediction using group-of-fields, distributed intra (I) and predictive (P) fields, and reduced I and P fields. Furthermore, Normille, et al. describe removing frame redundancy based on detected scene changes in sequence of moving images (U.S. Pat. No. 5,267,334), and compressed video encoding (U.S. Pat. No. 5,212,742). Additionally, U.S. Pat. Nos. 5,630,033 and 5,598,514 to Purcell, et al. describe MPEG encoder including motion estimation.
Prior art approaches at motion estimation, particularly for MPEG encoding process, are not structured optimally for semiconductor circuit implementation as well as providing low complexity. Therefore, there is a need to provide efficient algorithm and system for generating predictive motion vectors, particularly optimized for implementation as high-performance digital signal processor in integrated circuits.